The Role of a PQ type Calcium Channel Truncation Mutation in Epileptogenesis – Blog 1

Hello! My name is Zuleen Chia Chang and I am excited to work with Dr. Buraei on our research topic, “The Role of a PQ type Calcium Channel Truncation Mutation in Epileptogenesis”.

Voltage-gated calcium channels control neuronal excitability, muscle contractions and regulate calcium-sensitive signaling pathways. They play an important role as integral membrane proteins allowing calcium ions into the cell, which depolarizes the cell, and triggers calcium-dependent signaling. There are different types of calcium channels each with a different role, but the voltage-gated PQ type calcium channel plays a dominant role in synaptic transmission at central nervous sites. PQ type channels are often found in cerebellar granule cells. Cells contain various calcium sensitive proteins, such as enzymes that can be up or down regulated by the binding of calcium ions. Due to the broad effects of calcium channels, any small changes in calcium channel expression can induce pathophysiological changes in the brain. Mutations in the CACNA1A gene, which encodes the PQ channel, have been implicated in various diseases such as familial hemiplegic migraine, episodic ataxia type 2 and spinocerebellar ataxia type 6.

In addition, mutations in calcium channels are associated with epilepsy, which is characterized by recurring spontaneous seizures. However, it is unclear how these mutations alter PQ channel function. Thus, our purpose is to determine how mutant channels that cause epilepsy differ from wild-type channels in their function, which should point to better avenues for therapy. To study this, we have already introduced epilepsy-causing mutations into the wild-type (natural) human PQ channel using the QuikChange II XL Site-Directed Mutagenesis kit. But much more remains to be done if we are to test how the mutations impair channel function. Our current goal is to synthesize mutant and wild-type human PQ channel RNA. Once we have the RNA, we will inject the RNA into Xenopus oocytes to express the mutant and/or wild-type channel. Xenopus laevis oocytes have relatively few endogenous ion channels and can survive in vitro for several weeks. This will allow us to study wild-type and mutant PQ channel proteins by simulating a heterozygous genotype in an isolated environment. We will perform electrophysiological studies using two-electrode voltage clamp (TEVC) to compare the functions of wild-type and mutant PQ channels.

Epilepsy can be caused by hundreds of different mutations in different genes. Because of this diversity, most epilepsy drugs have severe side-effects and/or are not effective in many patients. However, with the advent of DNA sequencing technology, every family suffering from epilepsy can be genotyped and the specific mutations that presumably caused epilepsy can be, and have been, identified. But, to outline a course of treatment, it is critical to understand how the mutation impacts normal channel function. Our study of epileptic mutations in genes encoding the PQ channel will broaden our understanding of the development of epilepsy.